1. Technical Field
This application relates to testing of static random access memory (SRAM). More specifically, the application relates to the use of existing on-chip arrays for testing of the SRAM, especially in the system environment.
2. Description of Related Art
SRAM, short for static random access memory, is a type of memory that is faster and more reliable than the more common DRAM (dynamic RAM). The term static is derived from the fact that the memory doesn't need to be refreshed like dynamic RAM. SRAM give a faster access time and a shorter cycle time, compared to DRAM, although it is more expensive. Due to its high cost, SRAM is often used only as a memory cache.
It is common for many chips made by International Business Machines, Inc. (IBM), such as microprocessor chips containing SRAM caches, to have an automatic built-in self-testing (ABIST) circuits. However, unless the chip is connected to the probes of an advanced testing engine (ATE), it is possible only to test to the first failure and then the test will stop for lack of a place to store information. Not only is the ATE an expensive machine (about a million dollars), but it is also not a device that can be taken into the field to test a customer's computer when problems develop. It would be desirable to have a method for testing the SRAM on the chip in the field.